Experimental study of laser beam fluence fluctuation smoothing in asymmetric compressors

Fluence fluctuations on the fourth compressor grating limit the energy, power, and, ultimately, the focal intensity of ultra-high-power femtosecond lasers. Significant smoothing of output fluence fluctuations in various asymmetric compressors was demonstrated experimentally. The compressor symmetry was broken as a result of different angles of incidence of the beam on the first and third gratings in the horizontal plane, in the vertical plane, and in both planes simultaneously. Two-dimensional spatial spectra of the fluctuation suppression ratio were measured and proved to be in good agreement with the theory presented earlier. Specifically, if the angle of incidence on the third grating in the vertical plane is only 1 deg, the fluctuations with a scale of 2.5 mm or less are suppressed by two orders of magnitude.